Quantitative Microbial Risk Assessment of Pathogenic Vibrios in Marine Recreational Waters of Southern California

This study investigated the occurrence of three types of vibrios in Southern California recreational beach waters during the peak marine bathing season in 2007. Over 160 water samples were concentrated and enriched for the detection of vibrios. Four sets of PCR primers, specific for Vibrio cholerae, V. parahaemolyticus, and V. vulnificus species and the V. parahaemolyticus toxin gene, respectively, were used for the amplification of bacterial genomic DNA. Of 66 samples from Doheny State Beach, CA, 40.1% were positive for V. cholerae and 27.3% were positive for V. parahaemolyticus, and 1 sample (1.5%) was positive for the V. parahaemolyticus toxin gene. Of the 96 samples from Avalon Harbor, CA, 18.7% were positive for V. cholerae, 69.8% were positive for V. parahaemolyticus, and 5.2% were positive for the V. parahaemolyticus toxin gene. The detection of the V. cholerae genetic marker was significantly more frequent at Doheny State Beach, while the detection of the V. parahaemolyticus genetic marker was significantly more frequent at Avalon Harbor. A probability-of-illness model for V. parahaemolyticus was applied to the data. The risk for bathers exposed to recreational waters at two beaches was evaluated through Monte Carlo simulation techniques. The results suggest that the microbial risk from vibrios during beach recreation was below the illness benchmark set by the U.S. EPA. However, the risk varied with location and the type of water recreation activities. Surfers and children were exposed to a higher risk of vibrio diseases. Microbial risk assessment can serve as a useful tool for the management of risk related to opportunistic marine pathogens.